Radio mirror (Jan-Oct 1923)

u RADIO DIGEST ILLUSTRATED Mounting for Spider Web Coils Operating Dial Knobs Placed on Panel Front Unless spider web coils are neatly constructed they present an unsightly object on the front of a receiving set. Even if they are neatly wound they are so large WORKSHOP KINKS? EARN A DOLLAR— THERE are many little kinks worked out at home that would aid your fellow Radio worker if he only knew about them. There are new hook-ups, new ways of making parts and various unique ways of operating sets that are discovered every day. RADIO DIGEST is very much interested in securing such material. Send them in with full details, including stamped envelope so rejected copy may be returned. The work must be entirely original, not copied. RADIO KINKS DEPARTMENT, RADIO DIGEST, 123 West Madison St., Chicago, 111. tliey will extend out from the front and are in the way of the dial controls. It is always best to mount these coils on the inside of the case, but there is no suitable mounting for this purpose. The illustration shows a homemade device that controls the coils within the case 'by turning regular dial knobs on the panel front. The center coil is made stationary by fastening it in an upright position, the other two coils are hinged on like supports to the base surface. The control of the hinged members are obtained by eccentric disks attached to the dial shafts. Coil spTings are used to keep the hinged members against the eccentric — 2». S. Musser, Anderson, Ind. Inside Aerials There are many possibilities open to the Radio enthusiast who is unable to erect an-' outside aerial, and the conditions attending each are so varied that he should try every one before deciding upon the best. Where the set is located on the second floor or higher and a hallway fifty feet long or thereabout is available, four wires strung the full length will usually be the best sort of indoor aerial. The lead-in ECCENTRICS MOVE OUTSIDE COILS should then be taken from one end or from the middle, depending upon which is nearer the receiving set. All the wires should be joined at the lead-in. Another possibility in the way of an indoor antenna is the bedspring. Several springs may be joined together with better results, a good contact being obtained by tightening the end of the wire beneath one of the brass nuts on the framework. Often the antenna post may be connected to the gas pipe and the ground post to the radiator or water pipe and excellent results secured. Small Variable Condenser When an amateur is experimenting, he often finds need of an extra variable condenser but as the experiment is only slight, he does not make the purchase of one for the occasion. The condenser herein described is homemade and it will over Card BOARD come the difficulty. Procure two sheets of stiff paper, or cardboard of any convenient size, about 3 inches wide and 8 inches long'. Paste or shellac a sheet of tinfoil on each piece, leaving at the end about %-inch margin. In the center of this margin place a paper fastener so that the two parts will slide sideways on each other. Turn up the opposite end of the top plate, making %-inch of it stand at right angles to the base. Place a binding post in the center of the upright part and A. B. C. LESSONS (Continued from page 11) coupler and a variable condenser. As shown, the antenna is connected to one end of the primary coil L-l, while the ground connection is made to the center of the rotating switch S which moves over the points to which the taps of the primary are connected. Across the TO DETECTOR TO DETECTOR secondary of the coupler L-2 is connected the variable condenser C. The operation of the circuit is as follows: By means of the switch S, the wave length of the antenna system is adjusted to that of the desired incoming waves. As these incoming oscillations flow through L-l, they establish a pulsating magnetic field which as it expands and collapses cuts the turns of the secondary L-2 and induces in it electrical oscillations of the same nature and frequency as originally flowed in the primary circuit. In order that these oscillations in the secondary circuit may produce a maximum effect the closed circuit C-L-2 must be in resonance (have the same oscillation frequency) with the primary circuit. This is effected by adjusting the variable condenser C. Next the coupling between L-l and L-2 is adjusted by rotating the secondary until the sounds are heard in the receivers with maximum intensity. The detector circuit is then connected across the terminals A and B and the electrical oscillations set up across the condenser are then increased upon the detector. Variometer Used for Tuning' The use of a variometer for tuning purposes is clearly illustrated in Figure 26. Here the left hand part of the circuit is similar to that shown in Figure 25. The circuit is completed, however, by having connected across the points A B the Variometer V in series with the detector and the phones. The circuit is operated by first adjusting the switch S until the antenna system is tuned to the desired wave length. Next, the circuit L-2-C is thrown into resonance by adjusting the variable condenser C and the degree of coupling between L-l and L-2". After this has been accomplished the variometerdetector circuit is thrown into resonance by adjusting the position of the rotor of the variometer V. It is thus evident that with such completely tuned circuits maximum receiving efficiency is obtained. The variometer V in figure 26 tunes the circuit by altering the amount of inductance in it. If we compare the circuit illustrated-'in Figure 20 with that illustrated in Figure 26, we will at once see that the closed circuit in the former has no period of its own but must oscillate in unison with the waves coming from the antenna, while in Figure 26 the closed circuits are all perfectly tuned and will thus affect the detector with greater intensity. This completes our study of the tuning process of the receiving station, and we are now ready to consider the two final operations to be performed, namely, the Figure 26 action of the detector and the telephone receivers. Chapter Seven In chapter, seven, which is to appear in the next week's issue, we will make a detailed study of the crystal detector and how it serves to render the oscillations capable of affecting the telephone receivers so that audible sounds will be produced in accordance with those originally sent in to the transmitting station. Chapter seven will be of special interest because it will sum up in a practical manner the principles set forth in the last three chapters and apply them in the construction of an efficient receiving set. fasten another binding post on the end of the base piece. By simply sliding the plates on each other, the capacity may be varied. The maximum capacity of the condenser depends on the size of the plates. — John Barry, Cedar Rapids, Iowa. Amplifier Tube Condenser By using a fixed condenser of .0005 mfd. capacity across the grid and negative of the second stage amplifier tube the voice =^STA6Q AMPLIFIERS TUP>E and music will be much more natural and noises will be diminished to a great extent. A variable condenser will give slightly better results. This condenser used as described is of value, especially in loud talking instruments. — Arthur R. Klinger, Staunton, 111. Eliminating the Howl One way to prevent the howl in regenerative receivers is to put a shield around the detector tube. Such a shield can be made from a piece of cardboard tube 1% inches in diameter and 2% inches long, with its outside covered with tinfoil, and grounded. Place this over the tube. — Mike Kertz, Cleveland, O. Damp weather tends to shorten the useful life of any form of dry cell, including plate batteries, which should therefore be protected as much as possible. When your set does not seem to work while tuning in a station, do not blame the set but try another station. Some stations have poor modulation. REINARTZ ALL PARTS NECESSARY DEALERS: WRITE FOR DISCOUNTS 123 W.Madiron Jt.Chicaao 'CRYSTAL 1! j5> RECTIFIER MULTIPOINT (Patent Pending) A Synthetic CRYSTAL DETECTOR sensitive over its entire surface Eliminates all detector troubles. Extraordinary clearness and volume. Endowed by Radio experts and press. Sold in Sealed Packages only. Join the ever Increasing Kussnite fans. Price, Postpaid, mounted CrtSensitiveness guaranteed OwC RUSONITE CATWHISKER 14 Karat Gold Multiple Contact Super OC„ Sensitive *iOC Order from your dealer or direct from us, RUSONITE PRODUCTS CORP. 19 Park Row. N. Y. Efficient Circuit for Use with Indoor Aerial I have been experimenting for a long time on reception without an aerial and have at last come upon a circuit that is excellent for the indoor aerial type. This circuit is simple in construction when used with one step audio frequency. I find that stations can be readily copied at distances as great as 1500 miles with great ease and can be understood very plain. My first experiment was with a single insulated wire in the molding in my room with one step of Radio frequency but the results did not satisfy me and I changed my Radio frequency to, audio frequency and dropped an insulated number 18 wire from my set out over the window ledge until it remained about 1 foot from the ground. I was surprised at the results this produced and was able to copy with ease stations 700 miles distant, but still not being satisfied I next anchored an insulated wire at the top of my bed, passing it four times back and forth from head to foot of the bed and into the set. No change whatever was made in the circuit. My results were so much better than the previous one that I always have used this type of aerial. When through I always disconnect the lead-in and wind it up on a spool which only takes a few minutes. The circuit as submitted is used with an ordinary one step audio frequency with 22 and 40 volts respectively on the plates and six volts on the filaments. — D. P. Metzgar. Signals come in better just at sundown and sunrise. PHANTOM-CIRCUIT Build Your Own. This marvel of mystery, using no loop, no aerial and no ground, brings in music instead of interference. We have heard stations 950 miles distant on one tube. By using WD-11 tube set can be entirely self contained. Very easy to build from our instructions, use your own spare parts, nothing complicated like radio frequency or super regenerative. Only one tuning control. Complete instructions, with Lookup and photo of circuit mailed to you for 60 cents. Stamps accepted. VESCO RADIO SHOP. Box D-704. Vacaville. Ca I if . SWELLS EVERY NOTE INTO FULL RICHNESS MAKES YOUR OUTFITS COMPLETE WITH BALDWIN PHONES Type C Unit, . $11.00 Type C Head Set. $17.00 AT ALL GOOD DEALERS •HELTON •LOUDSPEAKER E STATES ELECTRIC COMPANY, Agents 24 Clinton Street Newark, N. J fOL^ftW BETTER LOUD SPEAKER $Q.85 £#•>!??!*' TRUE CABINET TYPE O Not just a common horn built into a cabinet. Beautiful — Compact—THE TONE OF FINE CABINET PHONOGRAPHS. ifel?^ your tw°-steP set a HOME ENTERTAINER. All SPI ROLAS are of the best construction, with fine, rubbed finishes and are absolutely guaranteed. SPIROLA DUPLEX— uses any headset. Satin black (DB) finish $3.85. Oak (DO) or mahogany (DM) finish $4.85. SPIROLA SIMPLEX— uses Baldwin or other unit Black (SB), oak (SO), mahogany (SM) flnisk, same prices as DUPLEX. SPIROLA CONCERT— complete -with and cord. Oak (CO) or mahogany $12.50. At dealers or postpaid (C. 0. D. if preferred) built-in unit (CM) finish E. H. DONNEEE MFG. CO., DEPX. D, BOX 70, ANN ARBOR, MICH.